I’ve got the same issue in 4.10 and this is a complete show-stopper for me. Any change to my meshes and I can delete all meshes, reassign all textures, rename all meshes, place all meshes (i.e. very nearly build my map from scratch).
It’s even worse with animation clips. The first import correctly imports 20 individual animations, but any change to the FBX file means the UE4 editor will import the first clip in the file 20 times, destroying my whole animation setup.
Combine this with the general slowness of the editor and blocking progress windows and the tiniest tweak to a texture coordinate becomes 4-6 hours of work :-/